The present invention relates to a motor apparatus and, more particularly, to a motor apparatus suitable for use as a brushless multiphase motor in which the rotation speed of a rotor is electrically controlled.
There has been well known, as a typical kind of brushless multiphase motor, the Hall motor in which the rotation of a rotor is detected by a Hall element and the detected result is used to generate a rotating magnetic field around the rotor. Namely, the rotational position of the rotor is detected by the Hall element and this detected result is used to sequentially supply drive current to plural poles (or phases) arranged around the rotor. Sequential supply of this drive current is achieved by a switching circuit. The rotating magnetic field thus generated serves to give a rotational force to the rotor.
A rotating magnetic field is generated by a switching circuit as described above, and the efficiency of the circuit itself which serves to drive poles of a motor is therefore high in the conventional motor apparatus. However, in the case of the conventional brushless motor typically represented by the Hall motor, the rotation control of the motor is attained by changing the supply voltage (or current) common to each of the poles of the motor. Namely, the rotation of the rotor is controlled by changing the magnitude of the drive current generated by a switching operation. Therefore, a nonsaturated type current amplifier (or class A amplifier) is needed to control the drive current, so that the high efficiency attained by the switching operation is offset by the low efficiency of the non-saturated type current amplifier, thus preventing the conventional motor apparatus from being made highly efficient.